Foams composed of polyurethane, polyvinyl chloride or the like have been used as a foam excellent in its flexibility and cushioning characteristics, and foams composed of polystyrene, polyethylene, polypropylene or the like have been used as a foam excellent in its thermoformability.
Methods for producing polyethylene foams are disclosed in, e.g., Japanese Patent Publication No. 41-6278. There is, however, a problem that the foam produced by this method does not provide soft cushioning characteristics, although it is excellent in thermoformability such as vacuum molding.
As a method of producing thermoplastic polyurethane foams, a chemical foaming method using a thermally decomposable foaming agent, such as azodicarbon amide, is known which is disclosed in Japanese Patent Laid-Open No. 7-157588.
In the chemical foaming method, however, thermoplastic polyurethane is partly decomposed and foamed to deteriorate the cells, and it is difficult to produce foams with a high molecular weight.
Therefore, foams excellent in all of elongation set, hysteresis, cell uniformity and heat resistance are desired. Simple methods of producing such foams, and molded articles and laminates thereof are also demanded.
It is an object of the present invention to provide a foam excellent in elongation set, hysteresis, cell uniformity and heat resistance, more particularly a foam obtained from a composition containing a thermoplastic polyurethane (including a composition composed of a 100% thermoplastic polyurethane, hereinafter referred to as a thermoplastic polyurethane composition, unless otherwise stated). It is another object of the present invention to provide a method for producing the above-described foam. It is still another object of the present invention to provide a molded article or laminate of the above-described foam.
The present invention also provides a method of easily foaming the thermoplastic polyurethane composition.